A self-tanning cosmetic composition containing dihydroxy acetone (hereinunder referred to as "DHA" is intended to color the skin as if it were tanned without being exposed to the sun (ultraviolet), and various products are commercially available.
Those products are required to be uniformly applied to the skin in order to prevent uneven coloring. They are generally produced in the form of an emulsified product such as cream with the stability of the product containing DHA taken into consideration.
On the other hand, since a self-tanning cosmetic composition which does not contain oil can color the skin in a shorter time, a prescription of a lotion which does not contain oil and is mixed with DHA is proposed with importance set on a coloring ability to the skin.
However, since such a lotion does not spread well on the skin, uniform application is difficult, which results in uneven coloring of the skin. In other words, the finish in self-tanning is apt to be greatly damaged.
In addition, an aqueous self-tanning lotion has such a low viscosity that it often drips and causes unevenness in the color when it is applied to the skin. That is, since there is a great problem in the finish in self-tanning, the commercialization of the aqueous lotion is difficult.
In order to eliminate the problem in a self-tanning lotion such as dripping and uneven coloration, attempts have long been made to add a thickening agent to a self-tanning lotion so as to increase the viscosity.
For example, a method of adding a thickening agent which is represented by sodium polyacrylate (Carbopole 940, Carbopole 941, etc. produced by B.F.GOODRICH) to a prescription containing DHA has been investigated. However, this produces a great problem in the guarantee of the quality, because, for example, the stability of the viscosity with time is greatly lowered due to the decrease in the pH caused by the addition of DHA, and the external color of the product changes to brown with time.
In contrast, it is possible to prevent the color of a self-tanning lotion from changing to brown by using a nonionic thickening agent. In this case, however, it is also impossible to suppress the lowering of the viscosity with time. In addition, since the thickening effect of a nonionic thickening agent is much lower than that of a polyacrylate thickening agent, it is necessary to add a large amount of nonionic thickening agent to obtain the same viscosity. In this case, the product becomes tacky, which is peculiar to a polymer and produces an unpleasant feeling when applied to the skin.